How many groups and periods are present in the modern periodic table?
The vertical columns in a periodic table are called groups and there are 18 groups in the long form of periodic table.The horizontal rows of elements in a periodic table are called periods and there are 7 periods in the long form of periodic table.
The family of elements having seven electrons in the outermost shell is ______.
The halogens are located on the left of the noble gases on the periodic table. These five toxic, non-metallic elements make up Group 17 of the periodic table and consist of: fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At). Although astatine is radioactive and only has short-lived isotopes, it behaves similar to iodine and is often included in the halogen group. Because the halogen elements have seven valence electrons, they only require one additional electron to form a full octet. This characteristic makes them more reactive than other non-metal groups.
Elements having same valence electrons are placed in same group but there is an exception with-
All the elements of group 18 have 8 valence electrons each in their atoms, except helium which has only 2 valence electrons in its atom as its duplet is complete.
Which is true about noble gases?
A. The do not react with other elements
B. They have completely filled outer most shells
C. Xenon is most reactive noble gas
D. Most of the them are radioactive
Due to their stable inert gas configuration, they are highly unreactive. Therefore, both statements (A) and (B) are correct.
Electropositive character of elements in a period ___________ from left to right.
As we move from left to right in a period, the positive charge increases due to gradual increase in the number of protons. So, the valence electrons are pulled in more strongly by the nucleus and it becomes more and more difficult for the atoms to lose electrons. Thus, on moving from left to right in a period, the tendency of atoms to lose electrons decreases i.e electropositive character of elements decreases.
The second ionization energy is greater than the first because
When one electron has been removed from the neutral gaseous atom, the positively charged ion formed has one electron less than the number of protons in the nucleus. As a result, the electrostatic attraction between the nucleus and the remaining valence electrons increases. Therefore, the second ionization enthalpy is greater than the first one.
P, Q, R are elements of Dobereiner’s triads. If the atomic mass of P is 7 and that of Q is 23, What will be the atomic mass of R?
According to Dobereiner's law of triads, when elements are arranged in the order of increasing atomic masses, groups of three elements having similar chemical properties are obtained. The atomic mass of the middle element of the triad is equal to the arithmetic mean of the atomic masses of the other two elements.
Which of the following is isoelectric with O2−
Isoelectronic ions are those which contains the same number of electrons.
O2- = 8+2 = 10 electrons
N3- = 7+3 = 10 electrons
Na+ = 11-1 = 10 electrons
F- = 9+1 = 10 electrons
How does the valency vary in going down a group?
Since the number of vallence electrons in a group is the same, all the elements in a group have the same valency.
The atomic number of an element is 16. Predict the nature of the element.
As the atomic number is 16, therefore, the valence electrons will be 6.
To complete its octet, it will gain two electrons and so will exhibit Non-metallic character.
Which element was discovered after Mendeleev gave the periodic table?
Mendeleev left proper gaps in his periodic table for the then undiscovered elements, and when Gallium(Ga) was discovered it was placed in one of those gaps without disturbing the existing elements.
Which of following statement is correct about isotopes?
A. Isotopes of an element have same atomic masses
B. Isotopes of an element have same atomic number
C. Isotopes of an element have same chemical properties
D. isotopes of and element have different atomic numbers
Isotopes of an element are the atoms with same atomic number but different atomic masses. Being the atoms of the same element, they possess similar chemical proeprties.
3517Cl and 3717Cl are the isotopes of Chlorine.
An element P belongs to the second period and group 13. What is the formula of its oxide?
The valency of the element of group 13 is 3, (13-10=3)
and oxygen has the valency of 2. So, formula of the oxide will be P2O3.
Which type of compound is formed by the elements of group 1 and group 17?
Elements of group 1 can readily lose 1 electron to complete their octet.
Elements of group 17 need one electron to complete their octet. So, both of them combine with each other and form ionic compounds.
An element with atomic no 3 combines with another element with atomic number 17, What would be the formula of the compound?
An element with atomic no 3 has electronic configuration 2,1 i.e. it can lose one electron readily to complete its duplet.
The element with atomic no 17 has electronic configuration 2,8,7 and is ready to accept one electron to complete its octet.
So, both of them with valency 1 combine and the formula is LiCl.
Which of the following is an example of Dobereiner's triad?
A. Li, Na, K
B. Cl, Br, I
C. Na, Mg, Al.
D. F, I, Br
According to Dobereiner's law of triads when elements are arranged in the order of increasing atomic masses, groups of three elements having similar chemical properties are obtained. The atomic mass of the middle element of the triad is equal to the arithmetic mean of the atomic masses of the other two elements.
Li, Na, K form the triad of alkali metals and Cl, Br and I form the triad of halogens.
What is the nature of an element having atomic number 20?
The element with atomic number 20 is Calcium(Ca) and it has metallic character as it loses it two valence electrons easily to complete its octet.
Give the symbol for the most reactive non-metal of group 17.
On going down the group of the periodic table, the electronegative character of non-metals decreases.
Therefore, Fluorine being on the top in group 17 elements have the most electronegative character.
Horizontal rows in a periodic table are called-
They are called Periods and we have seven periods in the long form of periodic table.
Which of the pairs of elements are members of the same group.
A. Na and K
B. Ar and Cl
C. Mg and Ca
D. O and S
Sodium and Potassium are the group 1 elements as they have 1 valence electron in their outermost shells.
Magnesium and Calcium are group 2 elements as they have 2 valence electrons in their outermost shells.
Which group elements are called transition metals?
The group 3 to group 12 elements are called Transition elements. In these elements, the outermost shell as well as the next to outermost shell are incomplete and in the process of being filled with electrons.
Which one has the bigger size?
The elements on the extreme left of the periodic table have the largest size.
K, being on the extreme left of all the elements given have the largest size as on moving from left to right in a period, the size of atoms decreases.
Which element has two shells both of which are completely filled with electrons?
Neon(Ne) with atomic number 10 has an inert gas configuration 2,8 where both the shells have completely filled electrons.
What property of all elements in the column of the periodic table as fluorine have in common?
All the elements of a group have the same number of valence electrons i.e Fluorine belongs to group 17 and all the elements have 7 valence electrons.
To complete their octet, they accept one electron readily and therefore they are electronegative elements with valency 1.
Electronic configuration of Al3+ is-
Electronic configuration of Al is 2,8,3
To form Al3+ , electronic configuration of Al is 2,8.
Element X forms a chloride with the formula XCl2 which is a solid with a high melting point. X would most likely to be in the same group of the periodic table as
This is because Mg has a valency of +2 and would easily give its two electrons to complete its outermost electronic configuration.
So, it combines with chlorine to form XCl2
Which of following statements is not true about hydrogen?
A. Oxides of hydrogen is neutral
B. it is placed in group 1 and Period 1
C. It is a metal
D. It has 1 electron, Proton and neutron
Hydrogen has an anomalous behaviour, it can behave as a metal as well as a non-metal.
It has 1 electron and 1 proton but no neutrons.
Which elements are called as synthetic elements?
All the elements beyond atomic no 92 are prepared in laboratory and so are called as Synthetic elements.
Which of the following element forms dipositive ions very easily?
Electronic configuration of Mg is 2,8,2
To complete its octet, it will lose two electrons readily and form divalent ion, Mg2+.
Which of the following statement is not a correct statement about the trends when going from left to right across the periodic table.
On moving from left to right in a period, the electropositive character of element decreases i.e. it becomes difficult for elements to lose electrons and form positive ions.